I skipped the entire puzzle. I shot a portal next to where you get the ball and hopped down into the tunnel. After that, I shot a portal high onto the wall and simply hopped over the laser wall. Finished it in seconds.

Very nice map! The only problem I can see is the two white squares on exit side of the laser field. You can just shoot a portal at one through the field and another on your side to get out without ever doing the cube trick at the end.